Preservatives for photographic developers

ABSTRACT

The storage life of silver halide developer solutions is extended by the addition to the solutions of salts, esters and amides of plicatic acid.

United States Patent Karchmar et al.

[ Dec. 23, 1975 PRESERVATIVES FOR PHOTOGRAPHIC DEVELOPERS Inventors: Arthur Karchmar, Guttenberg; Leo Lawrence Nejelski, Jr., Tabor, both of NJ.

International Telephone and Telegraph Corporation, New York, NY.

Filed: July 22, 1974 Appl. No.: 490,361

Assignee:

References Cited UNITED STATES PATENTS 3,515,556 6/1970 Russell etal....'..-.t ..96/66R Howard et al 260/473 F Howard et al.... 260/473 F Howard et al 260/473 F Buchholz et al. 260/559 Primary Examiner-Mary F. Kelley Attorney, Agent, or FirmJames B. Raden; Harold J.

Holt

ABSTRACT The storage life of silver halide developer solutions is extended by the addition to the solutions of salts, esters and amides of plicatic acid.

14 Claims, No Drawings PRESERVATIVES FOR PHOTOGRAPHIC DEVELOPERS storage so that they are commonly discarded prior to their exhaustion through the processing of film. This problem is of particular significance to those who process limited amounts of films at spaced or infrequent intervals where both the cost and inconvenience involved is preparing fresh solutions are important considerations.

Previous attempts to extend film developer aging life have consisted primarily in the physical displacement of the air over the solution in the storage container. A commercially available aerosol preparation is an illustration of one such attempt. Such displacement methods do not prevent developer aging by oxygen already in solution. Some antioxidants have also been used, but as antifoggants rather than film developer preservatives.

It is a primary object of this inventionto provide a preservative for photographic developer solutions which effectively extends the storage life of such solutions. I

It is an additional object of this invention to provide a relatively simple and inexpensive process for extending the storage life of photographic developer solutions which has no significant effect on the quality of the film developed with the solutions.

It has been found that salts, esters and amides of plicatic acid act as preservatives when added to solutions for developing silver halide photographic material. The plicatic acid compounds produce no loss in film speed when addedto'such solutions and have no significant effect on the fog level of the developed film.

Plicatic acid is a polyphenolic compound obtained from aqueous extracts of western red cedar wood. Processes for its separation and recovery are described in US. Pat. No. 3,716,574, assigned to the present assignee. The salts and esters of plicatic acid are disclosed in US. Pat. Nos. 3,754,937 and 3,644,481, both assigned to the present assignee. The amides of plicatic acid are disclosed in copending US. application Ser. No. 316,056, filed 12-18-72, now US. Pat. No. 3,810,941 also assigned to the present assignee. Examples of plicatic acid esters and salts which are useful in the invention are sodium and potassium plicatate and lower alkly plicatates such as methyl, ethyl, n-propyl, iso-propyl and Z-butyl plicatate. Examples of useful amides are ethyl and n-propyl plicatamide. Plicatic acid itself has been found to be too highly'acidic to be useful it tends to neutralize and thus impair the effectiveness of the normally alkaline developer solution.

While manyof the foregoing salts, esters and amides have relatively limited water solubility, such limited solubility is adequate in the practice of this invention as long as the compounds are soluble in the relatively small proportions required. The amount of plicatic acid derivative used may, at the lower end, be any amount which is effective to extend the life of the developer. As little as 0.01% (0.1 grams/liter) has been found to be effective to extend the storage life of the solutions. The maximum amount of plicatic acid derivative is that which is soluble in the developer solution, normally about 0.5% (5 grams/liter). A preferred amount of the preservative is from 0.02 to 0.3% (.2 to 3 grams/liter). (Percentages of preservative, as used herein, are weight by volume, being 1000 grams/liter). It is preferable that the normally somewhat acidic plicatic acid derivative be neutralized or made slightly alkaline prior to addition to the alkaline developer solution. This may conveniently be done, for example, by adding sodium carbonate or other mild alkali to a water solution of the plicatic acid derivative to raise its pH to 7 or above, preferably about 7.5. Neutralization avoids alteration of the alkalinity of the developer and hence prevents degradation of the quality of the developed film. Developers (such as Eastman Kodak D-76) are commercially available as. premixed powders which the user dissolves in water to obtain the final developer solution. It is possible to obtain at least some of the plicatic acid derivatives in either neutral or slightly alkaline crystalline form which can be incorporated directly into such preparations.

Photographic developer solutions with which the preservatives of the invention are useful are well known in the art. They are chemical solutions widely used in developing exposed silver halide photographic materials and are described in detail, for example, in Photo- Lab-lndex, Henry M. Lester, published by Morgan and Morgan, Dobbs Ferry, N.Y., 1973 (published annually with quarterly supplements). A typical composition consists of aqueous solutions of a reducer which is the developing agent, an accelerator (an alkali), a stabilizer to inhibit aerial oxidation and a retardant to limit development of unexposed silver grain. Commonly used developing agents are hydroquinone, p-aminophenol or p-methylaminophenol sulfate. Useful accelerators are alkalis such as borax or sodium carbonate. A commonly used stabilizer is sodium ,sulflte. Potassium bromide is a frequencly used retardant. It should be understood that the foregoing compositions are merely illustrative.

In developing photographic paper, rather than photographic negatives, highly dilute comparatively alkaline EXAMPLE N-propyl plicatate was added to a commercially available developer solution (Eastmann Kodak D-76) of the following composition:

Grams P-methylaminophenol sulfate 2 sodium sulfite 100 hydroquinonc 5 borax 2 water (to make 1 liter of solution) The n-propyl plicatate was added as a 0.2% (wt/volume) stock solution in place of a portion of the water used to make up the 1 liter solution of developer. The stock solution was made by dissolving 8 grams of The optical density of a series of film negatives developed and tested in accordance with the procedures set forth above was determined. Table 1 shows the aeration time required for optical density of films developed n-propyl plicate in four liters of water maintained at from each of the developer solutions to reach 70% of 90C. The stock solution was cooled and adjusted to a the initial optical density. It also shows the percentage pH of 7.5 using a saturated solution of sodium carbonof such aeration time relative to the control as a meaated. sure of the increase in useful life obtained by the addi- Kodak Panatomic-X sheet film was exposed at ASA tion of the antioxidant. In Table 1, aeration times have ratings of 64 and 80 using a Kodak gray scale as the been prorated from different test runs so that the resubject. The film was then developed in the foregoing sults are directly comparable. Where antioxidant was solution in accordance with the manufacturers recomadded, the amount was 0.10%. mendations. Table I Comparative tests were run of a series of solutions prepared as above, both with and without the preserva- A Aeratloi Percent of ntioxidant Hours Control tlves of the invention. In addition, solutions were also 0 prepared, and tested where possible, containing six gfifi gfgggg 5;; commercially available antioxidants. To test storage 3 N propy|p1icmmide 5|] 4 life, the solutions were aerated by admitting filtered air yifi g xgigi through the bottom of the processing tanks for the 6:ThiodyiPrPOpi0nic acid 577 265 developers. Air flow was regulated using capillaries 7. Catechol 274 126 calibrated to give equal flow in the lines to the tank Samoqui 403 185 distribution tUbCS. Aeration was carried out at ambient Number of hours of aeration to reduce the maximum negative density to 70% of room temperatures. The color and height of the developers in the tank were checked daily, the latter being maintained at 9.0 inches above the gas distribution The results show that all of the plicatic acid derivatives tubes by the addition of distilled water to insure a conextended the aging life of the developer. It also shows stant hydrostatic pressure. that, at the 0.10% level, the other commercial antioxi- Negative film optical densities were measured with a dants also extended developer life. However, as will be photometer (blue sensitive probe) and a transmission shown below, thiodipropionic acid is not as effective as light source with a diffusion filter. Every step in the potassium plicatate when the porportion of additive is gray scale image, a portion of a neutral density gray increased to 0.20%. Moreover, both Catechol and Sancard image and an unexposed portion of each film was toquin have shortcomings, not shared with the plicatic measured. A sheet of unexposed and undeveloped film acid compounds. Catechol is a developer itself and thus was also cleared and measured to obtain a value for the part of the result may reflect this property, rather than base film density. This figure was then subtracted from increased developer life. Moreover, Catechol will afthe density of the unexposed portion of each film to feet the kinetics of the developer solution because of its obtain their fog densities. The combined base and fog developer activity, whereas the plicatic compounds will densities were then substracted from all gray scale not. Santoquin left an oily residue on the surface of the densities to obtain the values produced by the photosolutions making it objectionable for practical use. graphic emulsion alone. Fog, or negative density produced by factors other The following six commercially available antioxithan image exposure, is also an important factor in dants were also investigated for their comparative evaluating developers. High fog levels are undesirable value in extending the life of photographic developer because they reduce negative contrast and increase solutions. The last three of the antioxidants were found printing exposure time. A second series of tests was run unsuitable because of insufficient solubility. to include this factor in the evaluation of the developer 1. Thiodipropionic acid. solutions. Calculations were made of the ratio of the 2. Catechol. maximum density to fog density both initially and at 3. Santoquin (Monsanto NEO2-008) made up as aeration time intervals. Higher negative to fog density 45% (wt./vol.) antioxidant in propylene glycol and ratios were indicative of better solution performance. dissolved directly in developer. An oil residue re- Three groups of tests were performed and they are mained on the surface of the solution. separately grouped in the following table. The tests of 4. Butylated hydroxy toluene (BHT) solubility in Groups 1 and 2 containing 0.1% additive were aerated water (0.0575 gm./1.) was too low for comparative at a rate of 2.5 liters per minute. The tests of Group 3 tests. were aerated at 3.5 liters per minute in an attempt to S. Butylated hydroxy anisole (BHA) dissolved but reduce the time required to inactivate the solutions.

greasy residue remained in developer. Not used Where no results are listed, no measurement was possibeeause deposits formed on negatives after immerble because there was no measurable image. Thiodision in developer. proprionic acid was compared on both an equimolar 6. Nordihydroquiaretic acid dissolved but formed and equal percentage basis with potassium plicitate in turbid solution after neutralization which precipithe Group 111 results. tated on standing.

TABLE 11 Antioxidant Amount Negative Density to Fog Ratios Group 1 Aeration, Hours 0 121 235 340 436 1. None 16.57 14.27 6.85

2. N-propyl plicatate TABLE ll-continued Antioxidant Amount (7%) Negative Density to Fog Ratios Group 2 Aeration, Hours 0 304 393 441 535 l. N-propyl plicatateDJO 10.59 5.23 1.04 2. N-propyl plicatamide 0.10 8.70 5.47 4.33 0.49 3. Potassium plicatate 0.10 11.31 5.60 6.30 1.00 4. Thiodipropionic acid 0.10 9.32 6.29 7.67 9.08 8.03

Group 3 Aeration, Hours 0 120 257 346 1. None 13.69 13.03 10.51 2. Potassium Plicatate 0.20 17.14 16.52 11.20 15.52 3. Thiodipropionic acid 0.05 13.20 13.25 9.10 4. Thiodipropionic acid 0.20 15.07 1 1.02 8.04

The results of Table 11 indicate that at the 0.10% level, thiodipropionic acid performed better than the other compounds on the aerated solution. However, at the 0.20% level, potassium plicatate yielded consistently higher ratios than the solutions containing thiodipropionic acid at both the same concentration (0.20%) and the equimolar concentration (0.05%). Fresh solutions containing potassium plicatate also produced higher ratios than the unaerated solutions containing thiodipropionic acid. Potassium plicatate should, therefore, be capable of producing the most effective prolongation of useful developer life of any of the compounds tested at practical concentration levels.

The invention thus offers a relatively simple and economical method of increasing the working life of developer solutions. The invention is particularly significant where batches of films are processed at intervals and stored for prolonged periods between batches. It is accordingly applicable, not only to amateur photographic practice, but also to experimental laboratories, photographic studios and other processors using manual batch development as opposed to continuous machine processing.

We claim:

1. An aqueous solution for developing photographic material comprising a silver halide developing agent and as a preservative therefor a compound selected from the group consisting of salts, esters and amides of plicatic acid in an amount effective to extend the storage life of said solution, said amount being at least 0.01% on a weight/volume basis.

2. The solution of claim 1 in which the plicatic acid compound is neutralized to a pH of at least 7 prior to its addition to the solution.

3. The solution of claim 2 in which the plicatic acid compound is a salt.

4. The solution of claim 3 in which the salt is potassium plicatate.

5. The solution of claim 2 in which the plicatic acid compound is an ester.

6. The solution of claim 5 in which the ester is n-propyl plicatate.

7. The solution of claim 2 in which the plicatic acid compound is an amide.

8. The solution of claim 7 in which the amide is npropyl plicatamide.

9. The solution of claim 2 in which the amount of plicatic acid compound is from 0.1 to 5 grams per liter.

10. A process for extending the storage life of aqueous solutions for developing photographic materials comprising adding to said solution containing a silver halide developing agent a preservative compound selected from the group consisting of salts, esters and amides of plicatic acid in an amount effective to extend the storage life of said solution, said amount being at least 0.01% on a weight/volume basis.

1 l. The process of claim 10 in which the preservative compound is added as an aqueous solution of said plicatie acid compound neutralized to a pH of at least 7.

12. The process of claim 11 in which the preservative is potassium plicatate.

13. The process of claim 11 in which the aqueous solution is a stock solution.

14. The process of claim 11 in which the photographic material is photographic negative. 

1. AN AQUEOUS SOLUTION FOR DEVELOPING PHOTOGRAPHIC MATERIAL COMPRISING A SILVER HALIDE DEVELOPING AGENT AND AS A PRESERVATIVE THEREFOR A COMPOUND SELECTED FROM THE GROUP CONSISTING OF SALTS, ESTERS AND AMIDES OF PLICATIC ACID IN AN AMOUNT EFFECTIVE TO EXTEND THE STORAGE LIFE OF SAID SOLUTION, SAID AMOUNT BEING AT LEAST 0.01% ON A WEIGHT/VOLUME BASIS.
 2. The solution of claim 1 in which the plicatic acid compound is neutralized to a pH of at least 7 prior to its addition to the solution.
 3. The solution of claim 2 in which the plicatic acid compound is a salt.
 4. The solution of claim 3 in which the salt is potassium plicatate.
 5. The solution of claim 2 in which the plicatic acid compound is an ester.
 6. The solution of claim 5 in which the ester is n-propyl plicatate.
 7. The solution of claim 2 in which the plicatic acid compound is an amide.
 8. The solution of claim 7 in which the amide is n-propyl plicatamide.
 9. The solution of claim 2 in which the amount of plicatic acid compound is from 0.1 to 5 grams per liter.
 10. A process for extending the storage life of aqueous solutions for developing photographic materials comprising adding to said solution containing a silver halide developing agent a preservative compound selected from the group consisting of salts, esters and amides of plicatic acid in an amount effective to extend the storage life of said solution, said amount being at least 0.01% on a weight/volume basis.
 11. The process of claim 10 in which the preservative compound is added as an aqueous solution of said plicatic acid compound neutralized to a pH of at least
 7. 12. The process of claim 11 in which the preservative is potassium plicatate.
 13. The process of claim 11 in which the aqueous solution is a stock solution.
 14. The process of claim 11 in which the photographic material is photographic negative. 